الفهرس 
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Abstract
Antibiotic resistance is one of the biggest health problems nowadays. Antibiotic resistance limits the selection of therapeutic agents and increases the potential for treatment failure and adverse clinical complications, increase morbidity and mortality rates, with serious impact on individual, social and economic levels. Antibiotic resistance is spreading rapidly all over the world become a problem in both human and veterinary medicine.
Antimicrobial resistance is considered an ideal model for one health issue which clearly indicates that the human health is connected to animal and environment health. The use of antibiotics in animal production in sub-therapeutic dose for long periods proved to create ideal conditions for bacteria to acquire resistance. These resistance genes can be transmitted directly or indirectly to human through food consumption, thus food of animal origin are considered to be as a reservoir of these resistance genes representing an emerging health problem.
The aim of this study was to determine the prevalence of foodborne pathogens in milk and some dairy products sold in Alexandria governorate and study their antibiotic resistance and identification of antibiotic resistance genes.
A total of 360 samples of raw milk and dairy products were collected from the ten districts in Alexandria governorate (Montaza Than, Montaza Awl, Sharq, Wasat, El-Gomrok, Gharb, El-Agamy, Amrya Awl, Amrya Than and Borg El-Arab) from January 2016 to March 2017. Thirty six samples consist of 10 raw milk, 4 Kariesh cheese, 4 white cheese, 4 Ras cheese, 7 yoghurt and 7 cream samples were collected from each district.
Aerobic plate count was determined by pour plate technique. Total coliform and enumeration of E. coil were determined using most probable number technique. Moreover isolation and identification of Campylobacter spp., E. coli, Salmonella spp. and enumeration, isolation and identification of Staphylococcus aureus were carried out using conventional culture methods.
Antibiotic susceptibility of the isolated microorganisms was assessed against 12 antibiotics which widely used in human and veterinary medicine using disk diffusion method. E. coli isolates were also screened for the ability of ESBLs production using double disk synergy test.
E. coli isolate that showed phenotypic carbapenem resistance was assessed for the presence of carbapenemases producing genes. E. coli isolates showed phenotypic production of ESBLs were assed for the presence of genes encoded ESBLs production and S. aureus isolates showed resistance to cefoxitin, erythromycin and clindamycin, and gentamycin were assed for the presence of mecA gene, ermA and ermC, aacA-D, respectively, using PCR to address the mechanism of resistance.
The results could be summarized as follows:
1- Microbiological examination
- The mean values of aerobic plate count (as mean ± SD) were 7.11 ± 0.52, 7.87 ± 0.86, 6.47 ± 0.98, 6.54 ± 0.52, 4.08 ± 1.51 and 6.80 ± 2.58 log CFU/ml or g for raw milk, Kariesh cheese, white cheese, Ras cheese, yoghurt and cream samples, respectively.
- 100%, 95%, 80%, 50%, 71.4% and 84.2% of raw milk, Kariesh cheese, white cheese, Ras cheese, yoghurt and cream samples were contaminated with coliform with mean values (as mean ± SD) of 4.66 ±1.50, 4.22 ±1.77, 2.24 ±1.5, 1.49 ±1.75, 2.63 ±1.93 and 4.62±2.51 log MPN/ml or g, respectively.
- The mean values for presumptive E. coli enumeration (as mean ± SD) were 3.7±1.60, 3.81 ±1.93, 1.45 ±1.42, 1.21 ±1.61, 2.27 ±1.82 and 3.89 ±2.57 log MPN/ml or g for raw milk, Kariesh cheese, white cheese, Ras cheese, yoghurt and cream, respectively.
- Campylobacter spp. could not be detected in any sample. Whereas Salmonella spp. was detected in 4 out of 100 (4%) of raw milk samples, and 2 out of 70 (2.9 %) of cream samples.
- Biochemical tests identified that E. coli was isolated from 242 out of all the 360 (67.2%) tested samples. It was isolated from 84 of the 100 (84%) raw milk samples, 32 of the 40(80%) Kariesh cheese sample, 21 out of the 40 (52.5%) white cheese samples, 16 out of the 40 (40%) Ras cheese samples, 42 out of the 70 (60%) yoghurt samples and 47 out of the 70 (67.14%) of cream sample.
- Biochemical tests identified that S. aureus was isolated from 81 out of the 360 (22.5%) samples tested. It was isolated from 29 of the 100 (29 %) raw milk samples, 5 of the 40 (12.5%) Kariesh cheese samples, 22 of the 40 (55 %) white cheese samples, 4 of the 40 (10%) Ras cheese samples, 4 of the 70 (5.7%) yoghurt samples and 17 of the 70 (24.3 %) cream samples.- The mean values of Staphylococcus aureus count (as mean ± SD) were 0.64 ±1.03, 0.27 ±0.78, 1.67 ±1.62, 0.30 ±0.93, 0.09 ±0.40 and 0.55 ±1.02 log CFU/ml or g for raw milk, Kariesh cheese, white cheese, Ras cheese, yoghurt and cream samples, respectively.
- The samples obtained from Wasat , Montaza Than, Sharq, El-Gomrok and Amrya Awl districts had the highest bacterial load of the studied bacteria therefore they considered to be of poor hygienic quality followed by the samples obtained from Montaza Awl , Garb, Amrya Than and El-Agamy districts. The samples obtained from Borg El-Arab district were relatively better samples compared to those obtained from the other districts.>2- Antibiotic susceptibility test- Seventy one E. coli isolates out of the 242 (29.3%) were resistant to at least one of the antibiotics used. Seventeen isolates (7.0%) showed resistance to one antibiotic, 15 isolates (6.2%) showed resistance to 2 antibiotics whereas 39 isolates (16.1%) were MDR with resistance to 3 or more antibiotics.
- All the E. coli isolates were susceptible to azithromycin, cefoxitin, ciprofloxacin and gentamycin. The highest resistance was to tetracycline which was observed in 62 (25.6%) out of the 242 E. coli isolates, whereas 22.3%, 12.8 %, 10.3%, 7% and 4.5 % were resistant to ampicillin, streptomycin, co-trimoxazole, cefotaxime and chloramphenicol respectively. Only one E. coli isolate (0.4%) showed resistance to both of amoxicillin -clavulanic acid and imipenem.
- The most frequently reported MDR pattern for E. coli isolates was resistance to ampicillin, streptomycin, tetracycline and co-trimoxazole.
- Seventeen E. coli isolates had the ability of ESBLs production, and only one isolate was positive for carbapenemases production.- Two of the six Salmonella isolates were MDR; one isolate was resistance to ampicillin, co-trimoxazole, and chloramphenicol and the other isolate was resistance to ampicillin, tetracycline and streptomycin whereas the four remaining isolates were susceptible to all antibiotic tested.- Seventy six S. aureus isolates out of the 81(93.8%) were resistant to at least one of the antibiotics used. Sixteen (19.8%) isolates showed resistance to one antibiotic, 29 (35.8%) isolates showed resistance to two antibiotics whereas 31 (38.3%) isolates were resistant to 3 or more antibiotics.- All S. aureus isolates were susceptible to ciprofloxacin, co-trimoxazole, linezolid and vancomycin. The highest resistance was to penicillin which was observed in 74 isolates (91.4%) out of the 81 isolates, whereas 65.4%, 42% and 13.6% were resistant to tetracycline, cefoxitin and chloramphenicol, respectively. Erythromycin and clindamycin resistance was observed in 10 isolates (12.3%), 9 isolates were inducible clindamycin resistance and one isolate was constitutive clindamycin resistance. Resistance to gentamicin was observed in 8 isolates (9.9%).
- The most frequently reported MDR pattern for S. aureus isolates was resistance to penicillin, tetracycline and cefoxitin.
3- Detection of antibiotic resistance genes
- One E. coil isolate which showed phenotypic carbapenemases production was found to harbor the blaOXA-48 gene and negative for blaKPC.- All the 17 E. coli isolates which showed phenotypic ESBLs production were found to harbor one or more of the tested resistance genes. blaSHV gene was the most frequent
detected gene. Five isolates possessed blaSHV alone and 2 isolates possessed blaCTX-M gene alone, whereas one isolate possessed blaSHV and blaCTX-M together. blaTEM and blaSHV found in 3 isolates and blaTEM and blaCTX-M together were also found in 3 isolates, while 3 isolates contained all the 3 genes.- Thirty one out of the 34 suspected MRSA (S. aureus showed resistance to cefoxitin) found to harbor the mecA gene, whereas it could not be detected in the other 3 isolates.
- Seven out of the 8 S. aureus isolates which showed resistance to gentamycin were found to harbor the aacA-D resistance gene. All the 10 erythromycin resistant S. aureus harbor the ermC, whereas ermA could not detected in any of them.- ESBLs producing E. coli was detected in 17 out of the 360 exmained samples with prevelance of 4.7%. White cheese samples had the highest prevelance of 10% , followed by raw milk, cream, Kariesh cheese and Ras cheese with prevelance of 6%,5.7%,5%,2.5% , respectively, whereas it could not be detected in any yoghurt samples.
- The highest MRSA prevalence was reported in white cheese samples of 22.5% followed by raw milk, Ras cheese, cream, yoghurt and Kariesh cheese with prevalence of 11%, 7.5% 7.14% 2.9% and 2.5%, respectively. The overall prevalence of MRSA in the tested raw milk and dairy product samples was 8.6%.